Technical Field
The present invention relates to optical switching and, more particularly, to bias control in an optical switch with a large number of switch units.
Description of the Related Art
High-port-count optical switch fabrics are receiving increased interest in many environments, including datacenters, cloud computing, and high-performance computers. Existing switch fabrics are implemented using, e.g., micro-electromechanical systems or are integrated onto a single chip using, e.g., silicon photonics. Photonic integration is used to provide a smaller footprint, lower cost, and lower power consumption, and may include a large number of optical devices that need to be stabilized and controlled for proper operation.
The elementary switching element is an on-off device that routes an optical signal from one input to one output. The input/output port configuration may be, e.g., 1×2, 2×2, or 2×1 depending on switch matrix arrangement. However, to minimize the error rate and/or signal-to-noise ratio degradation of an optical signal transmitted through the switch fabric, each switching element includes low insertion loss and low optical crosstalk, which can be achieved only if each of the switching elements is biased correctly.
There are multiple causes for the bias point of a switching element to drift, such as temperature, stress, and aging, and initial bias can differ from one element to the next due to fabrication variations or imperfections.